Decreases in the output power of semi-conductor elements together with increases in the operating frequency of amplification devices are leading to the need to combine several elementary semi-conductor amplifiers so as to achieve the output powers required by certain applications in the microwave field. In particular, for an active Ku-band antenna and to obtain a sufficient power level, it is often necessary to combine several amplifier modules in an antenna grid cell whose dimensions are of the order of a few centimeters.
Contemporary power combining systems based on corporate or radial architectures using lines or waveguides do not make it possible to efficiently combine elementary amplifiers in a confined environment with a rectangular-waveguide output interface able to cooperate with the downstream devices.
In a corporate structure combining several amplifiers, the amplifiers are disposed in parallel to one another and aligned along one and the same axis. The input and output waveguides of the amplifiers, the divider and the combiner are also aligned along this same axis. In the Ku-band and in rectangular guide technology, the width of such an amplification device is mainly constrained by the considerable size of the rectangular guides of the combiner. Thus, by taking into account only the value of the interior dimension according to a cross-section of a standardized Ku-band rectangular guide, equal to 1.9 cm, the width of an amplification device comprising for example eight amplifiers is at the minimum eight times as large, i.e. greater than 15 cm. This width being much greater than the dimensional constraints of an application relating to an active Ku-band antenna, this technique is therefore not suited to this type of application. For applications to higher frequencies, the size of the rectangular guides decreases and the width of the amplification device is no longer imposed by the combiner but by the width of the elementary amplifiers, decoupling capacitors and polarizing ports of these amplifiers. This width is therefore also too considerable with respect to the grid cell of an active antenna.
The spatial combining technique such as developed in U.S. Pat. No. 5,736,908 comprises several amplifier modules disposed on plates, overlaid in a rectangular waveguide. The input signal generated by a single source is apportioned among the amplifier modules by virtue of the spatial distribution of the energy of the signal and is recombined at the output once it has been amplified in accordance with the same principle. This solution makes it possible to perform in a single step on the one hand the combining of the signals and on the other hand the transitions between the planar-technology lines and the rectangular-waveguide output interface. By virtue of these characteristics, it makes it possible to minimize the combining losses and the bulkiness of the structure. However, this combining technique, such as described in the prior art, exhibits drawbacks and limitations.
Indeed, the number of plates stacked in a rectangular waveguide and the number of associated amplifiers on one and the same plate decrease with the reduction in the size of the rectangular waveguides which is imposed by the increase in operating frequency.
For applications to high frequencies such as for example in the Ka-band, the standardized size of the rectangular guides is much smaller than the size of the amplifier modules, thereby making it necessary to have long transmission lines for linking the amplifier modules to the transitions of the spatial divider excited by a single source and to the transitions of the spatial combiner. These transmission lines are very penalizing in terms of losses and the dividing and combining efficiency is degraded. A structure with four plates would be the best adapted in terms of compactness for combining eight elementary amplifiers in the case of an active Ku-band antenna. However, in this configuration, this type of architecture exhibits unfavorable thermal management in respect of the plates located at the center of the structure and a lack of isolation between the combined amplifiers possibly giving rise in certain cases to an instability of the amplification device.
Document WO 2006096771 describes another spatial combining technique in which the axes of the amplifiers are disposed along a direction perpendicular to the input and output waveguides, but for applications to high frequencies, in the Ka-band for example, the long input transmission lines are penalizing in terms of division losses.